Structure reinforcing method, structure-reinforcing reinforcing fiber yarn containing material, reinforcing structure material and reinforced structure

ABSTRACT

A method for reinforcing a structure with a sheet containing reinforcing fiber yarns is disclosed, by which method separation of the sheet is sufficiently prevented, maximum use of the sheet strength is achieved, and existing structures are effectively reinforced. The method includes the step of providing a sheet containing reinforcing fiber yarns over the surface of a structure selected from the group consisting of concrete and steel structures, with a flexible material interposed therebetween, the flexible material having a tensile elongation of 10 to 200% at maximum load at 23° C., and a tensile strength of 0.1 to 50 N/mm 2  at 23° C.

FIELD OF INVENTION

[0001] The present invention relates to a method for reinforcingconcrete or steel structures, such as beams, columns, slabs, walls,stacks, RC beams, slabs, railway tunnels, road tunnels, mountaintunnels, aqueduct tunnels for hydroelectric power stations, headracetunnels, pressure headrace tunnels, various other tunnels, undergroundstructures such as Hume pipes which are subjected to stress such asinternal and/or external pressure, bridges having a curved surface, andU-shaped gutters, by means of a sheet containing reinforcing fiberyarns. The present invention also relates to sheets containingreinforcing fiber yarns for use in the above reinforcing method,structure reinforcements, and reinforced structures reinforcedtherewith.

BACKGROUND OF THE INVENTION

[0002] There have recently been seen some concrete or steel structuresof which properties at the time of designing are no longer maintaineddue to deterioration of structural members over time. Reinforcement orrepair of such structures has been effected, such as reinforcement forimproving their earthquake-proof properties, repair for suppressingdeterioration of structural members, or reinforcement for improvingtheir functionality.

[0003] Conventional reinforcing methods include, for example, affixingsheets containing reinforcing fibers, such as reinforcing fiber sheetsand/or fiber-reinforced plastic plates, over the surface of a structureto be reinforced to integrate the sheet with the structure. Thisreinforcing method has been generally adopted with many successfulresults. On the other hand, methods for reinforcing a concrete surfaceof tunnel inner walls are also known, which include lining the outerconcrete surface with shotcrete or PC plates, and optionallyarch-setting with liner plates and H-steels, and splicing steel plates.Also known are methods for repairing or reinforcing headrace tunnels andthe like for resolving problems such as water leakage, decline instrength due to internal and external pressures, or decrease in actualwater delivery. These methods include, for example, a spraying methodwherein steel fiber-containing mortar or steel fiber-containing concreteis sprayed over the surface of the existing concrete lining, a paintingmethod wherein resin mortar or steel fiber-containing mortar is paintedover the surface, a casting method, and an affixing method.

[0004] Among the various methods mentioned above, for example, when themethod of affixing sheets containing reinforcing fibers over a structuresurface is performed using sheets that are hard to break and high intensile strength, the sheets provide excellent reinforcing effect, aslong as the sheets are fixed to the structure. In the final stage of thestructure life, however, the sheets containing reinforcing fibers tendto separate from the structure before they are broken, loosing thereinforcing effect, which ultimately leads to breakdown of thestructure.

[0005] For the purpose of overcoming such drawbacks, there have beenproposed methods for preventing separation of the sheets containingreinforcing fibers from the structure. Such methods include, forexample, providing an additional material containing reinforcing fibersfor fixing the sheets for reinforcement to the structure, or fixing thesheets to the structure by means of anchors or metal plates. With thesemethods, however, maximum use of the sheet strength is hard to beenjoyed, or the working process maybe complicated. Further, in the caseof tunnel structures having a curved surface, even a small displacementwill tend to cause separation of the sheets from the inner wall of thetunnel structure, and thus the reinforcing effect is hard to obtain.

[0006] There is also known a method wherein the sheets containingreinforcing fibers are stuck to the inner wall surface of a structurewith an adhesive. However, conventional adhesives are only for stickingthe sheets, and little cushioning effect is provided between the sheetsand the structure. Thus sufficient and long-lasting prevention ofseparation is not achieved. Incidentally, conventional adhesives canonly form a layer having a tensile elongation of less than 5% at maximumload at 23° C.

SUMMARY OF THE INVENTION

[0007] It is therefore an object of the present invention to provide amethod for reinforcing a structure with a sheet containing reinforcingfiber yarns, by which method separation of the sheet is sufficientlyprevented even when the sheet is provided on the surface of structuressuch as beams, columns, or RC beams, or on curved surfaces, maximum useof the sheet strength is enjoyed, and existing concrete or steelstructures are effectively reinforced.

[0008] It is another object of the present invention to provide, forreinforcing a structure with a sheet containing reinforcing fiber yarns,a structure-reinforcing sheet containing reinforcing fiber yarns and astructure reinforcement utilizing the same, which are effectivelyprevented from being separated, exhibit the maximum strength, and aresuitable for easy and sufficient reinforcement.

[0009] It is still another object of the present invention to provide areinforced structure of concrete or steel of which strength anddurability are reinforced.

[0010] According to the present invention, there is provided a methodfor reinforcing a structure comprising the step (A) of providing a sheetcontaining reinforcing fiber yarns (sometimes referred to as sheet (a)hereinbelow) over a surface of a structure selected from the groupconsisting of concrete and steel structures, with a flexible materialinterposed therebetween, said flexible material having a tensileelongation of 10 to 200% at maximum load at 23° C., and a tensilestrength of 0.1 to 50 N/mm² at 23° C.

[0011] According to the present invention, there is also provided astructure-reinforcing sheet containing reinforcing fiber yarns, whereinsaid structure-reinforcing sheet is sheet (a) for use in the reinforcingmethod mentioned above, and comprises a reinforcing material having aplurality of longitudinal reinforcing fiber yarns arranged parallel toeach other in a longitudinal direction of said sheet.

[0012] According to the present invention, there is also provided astructure reinforcement for reinforcing a structure selected from thegroup consisting of concrete and steel structures, said reinforcementcomprising a flexible material layer and sheet (a), said flexiblematerial layer having a tensile elongation of 10 to 200% at maximum loadat 23° C., and a tensile strength of 0.1 to 50 N/mm² at 23° C.

[0013] According to the present invention, there is further provided areinforced structure wherein the structure reinforcement mentioned aboveis provided over a surface of a structure selected from the groupconsisting of concrete and steel structures, with a flexible materiallayer of said structure reinforcement interposed between the surface ofthe structure and a sheet containing reinforcing fiber yarns of thestructure reinforcement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a schematic perspective view showing an embodiment of areinforcing material for a sheet containing reinforcing fiber yarnsaccording to the present invention.

[0015]FIG. 2 is a schematic perspective view showing another embodimentof a reinforcing material for a sheet containing reinforcing fiber yarnsaccording to the present invention.

[0016]FIG. 3 is a schematic perspective view showing yet anotherembodiment of a reinforcing material for a sheet containing reinforcingfiber yarns according to the present invention.

[0017]FIG. 4 is a schematic perspective view showing still anotherembodiment of a reinforcing material for a sheet containing reinforcingfiber yarns according to the present invention.

[0018]FIG. 5 is an illustration for explaining an embodiment of areinforcing method according to the present invention.

[0019]FIG. 6 is an illustration for explaining another embodiment of areinforcing method according to the present invention.

[0020]FIG. 7 is an illustration for explaining an embodiment of areinforced structure according to the present invention, which is aconcrete structure having a curved surface on its inner wall.

[0021]FIG. 8 is an illustration for explaining how to reinforce a testpiece used in the tests in Examples 1-1 to 1-4 and Comparative Examples1-1 to 1-3.

[0022]FIG. 9 is a graph showing the strain distribution of a sheet usedin Example 1-1.

[0023]FIG. 10 is a graph showing the relationship between the appliedload and the displacement in the tests in Examples 1-1 and 1-3, andComparative Examples 1-1 and 1-2.

[0024]FIG. 11 is a graph showing the strain distribution of the sheetused in Comparative Example 1-2.

[0025]FIG. 12 is an illustration for explaining how to reinforce a testpiece used in the tests in Examples 2-1 to 2-2 and Comparative Examples2-1 to 2-2.

[0026]FIG. 13 is a schematic front view of the apparatus and thereinforced concrete structure used in the loading test in Example 3-1and others.

[0027]FIG. 14 is a schematic side view of the apparatus and thereinforced concrete structure of FIG. 13.

[0028]FIG. 15 is a schematic front view of the apparatus and thereinforced semicylindrical concrete structure used in the loading testin Example 3-2 and others.

[0029]FIG. 16 is a schematic side view of the apparatus and thereinforced semicylindrical concrete structure of FIG. 15.

PREFERRED EMBODIMENTS OF THE INVENTION

[0030] The reinforcing method according to the present inventionincludes the step (A) of providing sheet (a) over a surface of aconcrete or steel structure, with the particular flexible materialinterposed between the surface and the sheet.

[0031] When the structure to be reinforced is, for example, a column orstack, step (A) is preferably providing sheet (a) over the outer surfaceof the structure, with the particular flexible material interposedtherebetween, so that, when reinforcement against bending is principallyintended, the reinforcing fiber yarns of sheet (a) are arranged in thelongitudinal or axial direction of the structure or in the direction ofthe tensile stress to be generated, whereas when reinforcement againstshearing is principally intended, the reinforcing fiber yarns arearranged in the circumferential direction or at right angles to theaxial direction of the structure or in the direction of the shearingstress to be generated.

[0032] When the structure to be reinforced is a beam or RC beamstep (A)is preferably providing sheet (a) over the surface of the structure,with the particular flexible material interposed therebetween, so that,when the reinforcement against bending is principally intended, thereinforcing fiber yarns of sheet (a) are arranged in the longitudinal oraxial direction of the structure or in the direction of the tensilestress to be generated, whereas when the reinforcement against shearingis principally intended, the reinforcing fiber yarns are arranged in thecircumferential direction or at right angles to the axial direction ofthe structure or in the direction of the shearing stress to begenerated.

[0033] When the structure to be reinforced is a deck or a slab, step (A)is preferably providing sheet (a) over the upper and/or lower surface ofthe structure, with the particular flexible material interposedtherebetween, so that, when the reinforcement against bending isprincipally intended, the reinforcing fiber yarns of sheet (a) arearranged in the longitudinal or axial direction of the structure or inthe direction of the tensile stress to be generated, whereas when thereinforcement against shearing is principally intended, the reinforcingfiber yarns are arranged in the transverse direction or at right anglesto the axial direction of the structure or in the direction of theshearing stress to be generated.

[0034] When the structure to be reinforced has no reinforcing steeltherein, sheet (a) may be arranged in any suitably selected direction.

[0035] When the structure to be reinforced has a curved surface on itsinner wall, step (A) is preferably providing sheet (a) at least over thecurved surface on the inner wall of the structure, with the particularflexible material interposed therebetween, so that the reinforcing fiberyarns of sheet (a) are arranged along the curvature of the curvedsurface.

[0036] When the structure to be reinforced has an annular inner wallsurface, step (A) is preferably providing sheet (a) continuously in thecircumferential direction of the inner wall surface over at least aportion of the length of the structure, with the particular flexiblematerial interposed therebetween, so that the reinforcing fiber yarns ofsheet (a) are arranged in the circumferential direction of the annularinner wall.

[0037] Sheet (a) used in step (A) for reinforcing a particular structuresuch as those mentioned above, may preferably be a sheet containing areinforcing material shown in FIG. 1, 2, or 4 to be discussed later.

[0038] The flexible material may be a material containing athermosetting or thermoplastic resin, or mixed resins thereof. Thethermosetting rein may be, for example, an epoxy, methylmethacrylate, ormethacrylate resin, or mixtures thereof. The thermoplastic resin may be,for example, a nylon, polycarbonate, polyurethane, polyethylene, orpolypropylene resin, or mixtures thereof.

[0039] The resin contained in the flexible material preferably has, whencured alone, a tensile modulus of elasticity of 0.1 to 50 N/mm², morepreferably 0.5 to 10 N/mm² at 23° C. The tensile modulus of elasticitymay be measured in accordance with JIS K7113. The content of the resinin the flexible material is usually 50 to 100 wt %, preferably 59 to 98wt %, more preferably 70 to 80 wt %.

[0040] In order to maintain the flexible material within a suitablerange of viscosity for forming a flexible material layer, or to preventsagging of the material for facilitating application to the structure,the flexible material may optionally contain a filler or a thixotropicagent as desired in addition to the resin, as long as the objects of thepresent invention are achieved. Addition of a filler will slightlydecrease the tensile elongation at maximum load of the flexiblematerial, but the tensile strength and the tensile modulus of elasticitywill be improved.

[0041] The filler may be, for example, carbon black, calcium carbonate,talc, silic acid, silicate, or an inorganic pigment such as white lead,red lead, chrome yellow, titanium dioxide, strontium chromate, titaniumyellow, or other pigment. The content of the filler in the flexiblematerial is usually 0 to 50 wt %, preferably 1 to 40 wt %, morepreferably 10 to 20 wt %.

[0042] Thixotropic agents have organic and inorganic types. Among theinorganic thixotropic agents, for example, fumed silica, smectite clayminerals, swelling mica, synthetic smectite, bentonite, carbon black,and hectorite may preferably be used. The content of the thixotropicagent in the flexible material is usually 0 to 50 wt %, preferably 1 to40 wt %, more preferably 10 to 20 wt %.

[0043] The flexible material has a tensile elongation of 10 to 200%,preferably 10 to 100%, at maximum load at 23° C. In applying a startingmaterial for the flexible material to the surface of a structure,undesirable sagging of the material may occur, which may sometimes beprevented by setting the tensile elongation at maximum load at a lowervalue. On the other hand, it is particularly preferred that the flexiblematerial has a larger tensile elongation at maximum load than that of aresin in sheet (a) or a matrix resin for sticking sheet (a), whichresins will be discussed later. The tensile strength of the flexiblematerial is 0.1 to 50 N/mm² at 23° C. The tensile elongation at maximumload and the tensile strength of the flexible material may be measuredin accordance with JIS K7113.

[0044] By setting the tensile elongation at maximum load and the tensilestrength of the flexible material at 23° C., as well as the tensilemodulus of elasticity at 23° C. of the resin in the flexible material,if contained, to be within the above ranges, separation of sheet (a) isprevented, and maximum use of the strength of sheet (a) may be enjoyed.

[0045] It is particularly preferred that the flexible material has atensile elongation of 10 to 200%, more preferably 10to 100%, at maximumload at 5° C., and a tensile strength of 0.1 to 50 N/mm²at 5° C. It isalso particularly preferred that the resin contained in the flexiblematerial, if any, has a tensile modulus of elasticity of 0.1 to 50N/mm², more preferably 0.5 to 10 N/mm² at 5° C., when cured alone. Withsuch a flexible material that is capable of maintaining the abovematerial properties even at lower temperatures, excellent reinforcingeffect may be provided even under the cold conditions.

[0046] The flexible material may be selected from commercially availableproducts, such as EE50, EE50W, or EE60, all manufactured by TOHOEARTHTECH, INC.

[0047] The flexible material is provided in the form of a layer over thesurface of a structure to be reinforced either directly or via otherlayers optionally provided as desired, such as a primer layer. Thethickness of the flexible material layer is not particularly limited,and is usually 100 to 2000 μm, preferably 200 to 1000 μm.

[0048] The flexible material layer functions to disperse and transmitthe stress generated in the structure to sheet (a). The flexiblematerial layer may also be given improved adhesion to sheet (a) bymodifying its surface, i.e. the surface facing to sheet (a), through aphysical or chemical treatment, if desired. The physical treatment maybe surface roughening by grinding or with a sand paper, or ultrasonictreatment. The chemical treatment may be partial oxidation of thesurface or addition of functional groups to the surface, such as atreatment with corona, plasma, or an oxidizing agent. These treatmentsmay preferably be effected when, in particular, the flexible materialcontains a polyethylene or polypropylene resin, or the like resin.

[0049] The flexible material layer may be formed by (i) applying aliquid starting material for the flexible material over the surface of astructure to be reinforced and then curing the material, or (ii)affixing a material which has the flexible material and is formed into afilm, sheet, or the like shape, over the surface of a structure to bereinforced.

[0050] When the flexible material layer is to be formed by the abovemethod (i), a starting material for the flexible material is used whichexhibits, when cured, the particular tensile elongation at maximum loadand the particular tensile strength mentioned above. For example, astarting material composed of the various thermosetting and/orthermoplastic resins mentioned above, or the starting material furthermixed with the filler and/or the thixotropic agent, may be used. Here,as a thermosetting resin, a room temperature-setting type is preferredfor its good handleability. Two component resins are also preferred.

[0051] The thermosetting resin of a room temperature-setting typepreferably has, as a staring material for the flexible material, a potlife of 30 minutes to 5 hours, more preferably 30 minutes to 2 hours, at20° C. in view of handleability. The time required for curing a paintedlayer of the thermosetting resin at 20° C. is preferably 1 to 24 hours,more preferably 1 to 12 hours, in view of work schedule. The timerequired for the starting material for the flexible material to expressdesign strength is usually 1 to 20 days, preferably 1 to 7 days, at 20°C. The viscosity of the starting material for the flexible materialmeasured in accordance with JIS K6833 is usually 50 to 1000000 mPa.s,preferably 5000 to 300000 mPa.s, at 20° C. for facilitating application.

[0052] The starting material for the flexible material may be applieduniformly by means of roller brushes, rubber spatulas, trowels, or thelike tools, to have a desired thickness as mentioned above.

[0053] The starting material for the flexible material, when it containsa thermosetting resin, may be cured by heating to its curing temperaturewith a hot roller or a dryer, after application to the surface of astructure to be reinforced. When the starting material contains athermosetting resin of a room temperature-setting type, the startingmaterial may be cured simply by leaving the material to stand at a roomtemperature for a time period required for expression of its designstrength.

[0054] When the flexible material layer is to be formed by the abovemethod (ii), the starting material for the flexible material maypreferably contain a thermoplastic rein or a flexible thermosettingresin.

[0055] The material having the flexible material and formed into aparticular shape may usually be affixed by a suitably selectedconventional method, such as fusing with heat or sticking with anadhesive. The adhesive is preferably selected from those which arecapable of sticking the flexible material layer to a structure to bereinforced at a bonding strength higher than the strength of thestructure, and is preferably of the same kind of material as thestarting material for the flexible material.

[0056] Sheet (a) used in the reinforcing method of the present inventioncontains reinforcing fiber yarns. The reinforcing fibers in thereinforcing fiber yarns may be carbon fibers, glass fibers, ceramicfibers, aramid fibers, silicon carbide fibers, or combinations thereof,with carbon fibers being particularly preferred for their light weightand corrosion resistance. The carbon fibers may be pitch-based carbonfibers, polyacrylonitrile (PAN) -based carbon fibers, or combinationsthereof.

[0057] When the carbon fibers are required to have a high elasticity,pich-based carbon fibers may usually be used, such as XN60 manufacturedby NIPPON GRAPHITE FIBER CORPORATION. When the carbon fibers arerequired to have a high strength, polyacrylonitrile-based carbon fibersmay usually be used, such as T700SC or T300 both manufactured by TORAYINDUSTRIES, INC., UT500 manufactured by TOHO RAYON KABUSHIKI KAISHA, orTR30 manufactured by MITSUBISHI RAYON CO., LTD.

[0058] The reinforcing fibers are made into two-dimensional fabrics,unidirectional fabrics, or unidirectional material, which are used asthe reinforcing fiber yarns composing sheet (a).

[0059] Sheet (a) may be any material in the form of a sheet thatcontains reinforcing fiber yarns. This term is interpreted to includeplastic plates that contain reinforcing fiber yarns.

[0060] It is usually preferred that sheet (a) has a fiber area weight of100 to 800 g/m², 1000 to 10000 filaments per one reinforcing fiber yarn,a tensile strength of 2000 to 5000 N/mm², and a tensile modulus ofelasticity of 2×10⁵ to 1×10⁶ N/mm².

[0061] The sheet containing reinforcing fiber yarns according to thepresent invention is a sheet (a) which contains a reinforcing materialhaving a plurality of longitudinal reinforcing fiber yarns arrangedparallel to each other in a longitudinal direction of the sheet, whichsheet is referred to as sheet (1). Preferred examples of sheet (1) ofthe present invention may include the following sheets:

[0062] Sheet (2) wherein the reinforcing material of sheet (1) furtherhas a plurality of transverse threads arranged parallel to each other ina transverse direction of the sheet. The transverse threads aretransverse reinforcing fiber yarns and/or transverse supplementarythreads, and the longitudinal reinforcing fiber yarns and the transversethreads form a woven structure.

[0063] Sheet (3) wherein the longitudinal reinforcing fiber yarns andthe transverse threads in sheet (2) are stuck and fixed to each otherwith fixing members.

[0064] Sheet (4) wherein the reinforcing material of sheet (1) furtherhas a plurality of longitudinal supplementary threads arranged parallelto each other in the longitudinal direction of the sheet, and aplurality of transverse supplementary threads arranged parallel to eachother in the transverse direction of the sheet. The reinforcing materialhas a woven structure wherein the longitudinal reinforcing fiber yarnsare substantially not bent with the longitudinal and transversesupplementary threads.

[0065] Sheet (5) containing the reinforcing material of any one ofsheets (1) to (4) and a support for supporting the reinforcing material.The reinforcing material is affixed to the support by means of a binder.

[0066] Sheet (3) falling within the concept of sheet (2) may be, forexample, a cloth-like sheet wherein one of its warps and wefts are thereinforcing fiber yarns, and the other are supplementary threads made offibers containing a thermoplastic resin. The fibers containing athermoplastic resin may be fibers of a thermoplastic resin, or anyfibers having a thermoplastic resin or thermoplastic fibers stuckthereto. The warps and wefts are stuck and fixed to each other with thethermoplastic resin in the fibers containing a thermoplastic resin.

[0067] Sheet (5) may be, for example, a sheet which has the reinforcingfiber yarns arranged unidirectionally and a net-like lattice containinga thermoplastic resin. The lattice is mounted on and affixed to thesheet by means of the thermoplastic resin in the fibers containing athermoplastic resin.

[0068] Sheet (3) falling within the concept of sheet (1) or (2) may be,for example, a sheet containing reinforcing material 10 shown in FIG. 1.The reinforcing material 10 is a material which has a plurality ofreinforcing fiber yarns la arranged parallel to each other in thelongitudinal direction of the sheet, and a plurality of transversesupplementary threads 2 a. The yarns la and the threads 2 a cross overeach other to form a unidirectional reinforcing fiber fabric. Thereinforcing fiber yarns la and the transverse supplementary threads 2 aare stuck and fixed to each other with fixing members 3.

[0069] Sheet (3) falling within the concept of sheet (1), (2), or (4)may be, for example, a sheet containing reinforcing material 20 shown inFIG. 2. The reinforcing material 20 is a material wherein set (X) ofplurality of reinforcing fiber yarns la arranged parallel to each otherin the longitudinal direction of the sheet and oriented unidirectionallyin the form of a sheet, set (Y) of a plurality of transversesupplementary threads 2 a arranged on front and back sides of set (X),and set (Z) of longitudinal supplementary threads 2 b arranged at rightangles to set (Y) and parallel to set (X), form a woven fabric withoutsubstantially bending the reinforcing fiber yarns 1 a. The reinforcingfiber yarns 1 a, the transverse supplementary threads 2a, and thelongitudinal supplementary threads 2 b are stuck and fixed to each otherwith the fixing members 3 at appropriate locations.

[0070] Sheet (3) falling within the concept of sheet (1) or (2) may be,for example, a sheet containing reinforcing material 30 show in FIG. 3.The reinforcing material 30 is a bidirectional plain weave fabric ofreinforcing fiber yarns, wherein a plurality of reinforcing fiber yarns1 a arranged parallel to each other in the longitudinal direction of thesheet are arranged at right angles to a plurality of transversereinforcing fiber yarns 1 b. The longitudinal reinforcing fiber yarns laand the transverse reinforcing fiber yarns 1 b are stuck and fixed toeach other with the fixing members 3.

[0071] Sheet (5) falling within the concept of sheet (1) may be, forexample, a sheet containing reinforcing material 40 shown in FIG. 4. Thereinforcing material 40 is a material wherein mesh-like support 4 isaffixed by means of a binder 5 to one side of a sheet made of aplurality of reinforcing fiber yarns 1 a arranged parallel to each otherin the longitudinal direction of the sheet.

[0072] The material of the binder 5 is not particularly limited, and maybe selected from those similar to the materials for the matrix resin tobe discussed later. The amount of the binder 5 to be applied ispreferably 3 to 7 parts by weight based on 100 parts by weight of thereinforcing fiber yarns 1 a.

[0073] In the various reinforcing materials mentioned above, thelongitudinal reinforcing fiber yarns 1 a may be, or may not be, stuckand fixed to the transverse supplementary threads 2 a or transversereinforcing fiber yarns 1 b by means of the fixing members 3 made of,for example, a low-melting polymer. The fixing members 3 may becontained in advance in the longitudinal reinforcing fiber yarns 1 a,transverse supplementary threads 2 a, or transverse reinforcing fiberyarns 1 b.

[0074] The material of the fixing members 3 is not particularly limited,and may be, for example, nylon, nylon copolymers, polyester, vinylidenechloride, vinyl chloride, polyurethane, or mixtures thereof, with nyloncopolymers being particularly preferred. The transverse supplementarythreads 2 a and the longitudinal supplementary threads 2 b arepreferably made of glass fibers.

[0075] When a plastic plate is to be used as sheet (a), such a plasticplate may be prepared by impregnating the reinforcing material in theform of a two-dimensional fabric, unidirectional fabric, orunidirectional material, with a material containing a matrix resin, andcuring by heating into a plate shape.

[0076] The matrix resin may be a thermosetting or thermoplastic resin,or mixtures thereof. The thermosetting resin may be, for example, anepoxy, methylmethacrylate, or methacrylate resin, or mixtures thereof.The thermoplastic resin may be a nylon, polycarbonate, polyurethane,polyethylene, or polypropylene resin, or mixtures thereof, andpreferably has good adhesion.

[0077] According to the reinforcing method of the present invention,sheet (a) is provided over the surface of a structure to be reinforced,with the flexible material interposed therebetween. Here, sheet (a) maybe provided over the surface of the flexible material either directly orvia other layers optionally provided, such as an undercoating layer.

[0078] According to the reinforcing method of the present invention,other layers such as an overcoating layer and a finishing layer, mayoptionally be provided on sheet (a) For example, by applying a matrixresin material as an undercoating layer prior to the affixing of sheet(a), and applying the matrix resin material again as an overcoatinglayer after the affixing of sheet (a) , a composite layer of sheet (a)and the matrix resin may be obtained, which has a high strength. Whenthe plastic plate mentioned above is used as sheet (a), the plasticplate maybe affixed to the surface of the flexible material with anadhesive.

[0079] The thickness of sheet (a) is not particularly limited. Theelongation at break of sheet (a) may preferably be 0.5 to 3.0%, morepreferably 0.6 to 2.0%.

[0080] The concrete or steel structures to which the reinforcing methodof the present invention is to be applied, are not particularly limited,and may include various structures such as columns, beams, slabs, walls,RC beams, slabs, stacks, tunnels, pipes, tubes, ducts, conduits, bridgeshaving a curved surface, and U-shaped gutters. The structures to bereinforced include not only existing buildings, but also structures tobe made into buildings, such as concrete or steel parts as manufacturedat factories.

[0081] In the present invention, “reinforcing” means not onlyreinforcing of undeteriorated structures, but also repairing ofdeteriorated structures. The structures having a curved surfaceincludes, for example, structures having a longitudinally-extendingcurved surface with the radius of not smaller than 300 mm, whereas thestructures having an annular inner wall surface includes, for example,structures having an annular inner wall surface with the radius of notsmaller than 300 mm. Specifically, the structures having alongitudinally-extending curved surface on its inner wall or an annularinner wall surface which are constructed in the ground and placed understress such as internal and/or external pressure, may be included, suchas railway tunnels, road tunnels, mountain tunnels, aqueduct tunnels forhydroelectric power stations, agricultural aqueduct tunnels, headracetunnels for water supply and sewage works, headrace tunnels forindustrial water, headrace tunnels for tailraces for rivers, pressureheadrace tunnels, and Hume pipes.

[0082] A specific example of the working process of the presentreinforcing method includes, for example, sequentially forming eachlayer as desired on the surface of a structure to be reinforced, such asa primer layer, a flexible material layer, an undercoating layer, sheet(a), an overcoating layer, and a finishing layer. Of these layers, theflexible material layer and sheet (a) are essential, and the otherlayers may be formed optionally. These layers may usually be formedsequentially from the layer closest to the structure surface. In somecases, however, a structure reinforcement containing a composite of theflexible material layer and sheet (a) may be formed in advance, and thenaffixed to the surface of the structure.

[0083] An example of the reinforcing method of the present invention isexplained below with reference to FIG. 5.

[0084] Referring to FIG. 5, the numeral 11 refers to a structure to bereinforced. First, the surface of the structure 11 is pretreated asdesired, such as by cleaning. When the structure is made of concrete,steps or fractures on the surface may also be pretreated by grinding orwith a surface preparation material. The cleaning may be effected with adisc sander, waste cloth, or an organic solvent, or by sand blasting orhigh pressure washing.

[0085] The surface preparation material may be a resin having acompressive strength that is the same as or higher than the concretestrength, such as epoxy resin putty or epoxy resin mortar. The steps andfractures may be filled with such a resin in the pretreatment. It isalso preferred to round projected and recessed corners in thepretreatment step. When desired pretreatments are completed, thepositions of sheets (a) to be affixed may be marked as desired.

[0086] Next, primer is applied over the surface of the structure 11 witha roller brush or the like tool and dried to form primer layer 12. Theprimer may be a material having good adhesion to the structure 11 andflexible material layer 13, such as a solvent or non-solvent epoxyresin.

[0087] The mixing viscosity of the primer is usually 1 to 10000 mPa.s,preferably 10 to 5000 mPa.s at 20° C. in view of handleability.

[0088] The preferred temperature at which the primer is applied, isusually −10° C. to 50° C. The amount of the primer to be applied isusually 0.01 to 1 kg/m², preferably 0.1 to 0.5 kg/m². The time requiredfor drying the primer at 20° C. is usually 1 to 24 hours, preferably 1to 12 hours.

[0089] After the primer layer 12 is formed, a levelling material such asputty is optionally applied to smooth the unevenness of the primer layersurface, and then the flexible material layer 13 is formed thereon by amethod such as those mentioned above. Instead of applying the levellingmaterial such as putty, the flexible material layer 13 may be formed soas to smooth the unevenness of the primer layer surface. In this case,components of the levelling material may be added to the flexiblematerial as desired. After the flexible material layer 13 is formed, thesurface of the layer 13 may be modified as desired by a physical orchemical treatment. Then a matrix resin material or the like materialfor undercoating layer 14 may optionally be applied. The matrix resinmaterial may suitably be selected from the examples of the matrix resinmentioned above which has good adhesion to the flexible material.

[0090] The matrix resin material may contain, in addition to the resin,a suitable filler or thixotropic agent in order to maintain the materialwithin a suitable viscosity range or to prevent sagging uponapplication, as long as the objects of the present invention areachieved. Such filler and thixotropic agent may suitably be selectedfrom the examples listed above in the discussion of the flexiblematerial. The content of the filler and/or thixotropic agent in thematrix resin material is preferably 1 to 20 wt %.

[0091] When the matrix resin material contains a roomtemperature-setting resin, the pot life of the resin is preferably 30minutes to 5 hours, more preferably 30 minutes to 2 hours at 20° C. inview of the handleability of the matrix resin material. The timerequired for curing a painted layer of the matrix resin material at 20°C. is preferably 1 to 24 hours, more preferably 1 to 12 hours in view ofwork schedule.

[0092] The time required for the matrix resin material to express itsdesign strength is usually 1 to 20 days, preferably 1 to 7 days at 20°C. The viscosity of the matrix resin material is usually 10 to 100000mPa.s, preferably 100 to 50000 mPa.s at 20° C. in view of readiness topermeate and defoam.

[0093] The matrix resin material for the undercoating layer may beapplied by means of a roller brush, rubber spatula, or the like tool, sothat usually 0.1 to 2 kg/m², preferably 0.2 to 1 kg/m² of the materialis applied uniformly.

[0094] Next, sheet 15 as sheet (a) is affixed to the undercoating layer14. This step may include sticking the sheet 15 at the marked positionmentioned above immediately after the application of the material of theundercoating layer 14, and squeezing the surface of the sheet 15 with arubber spatula, hot roller, defoaming roller, or the like tool,preferably in the direction of the reinforcing fiber yarns, morepreferably from the center toward the edges of the sheet 15 along thereinforcing fiber yarns. By these steps, the sheet 15 is impregnatedwith the matrix resin material and the air bubbles in the sheet 15 areremoved, leaving a smooth surface.

[0095] In the step of affixing the sheet 15, too much length of thesheet 15 will disturb the operation. Thus the sheet 15 may be cut intoan appropriate length, and a plurality of the cut sheets may be splicedtogether. In this case, in order to provide a sufficient strength, it ispreferred to splice the sheets together with the overlap width of notless than 100 mm in the direction for ensuring the strength.

[0096] Next, a matrix resin material for overcoating layer 16 is appliedover the sheet 15. This step may include applying the same matrix resinmaterial as used in the undercoating step, by means of a roller brush,rubber spatula, or the like tool, so that usually 0.05 to 2 kg/m²,preferably 0.1 to 1 kg/m² of the material is applied uniformly.

[0097] In each of the above mentioned steps, it is preferred toimmediately remove blisters, wrinkles, and kinks of the fibers, if any.It is also preferred to provide sufficient protection against foulingand rain.

[0098] Finally, a finishing step is carried out. This step may includeapplying a weather-proof coating such as of a urethane resin orfluororesin, or a polymer cement material, over the overcoating layer 16to form a protective layer 17.

[0099] In the examples of the working process discussed so far, only onelayer of the sheet containing reinforcing fiber yarns is provided.However, in the present reinforcing method, two or more layers of thesheets containing reinforcing fiber yarns may also be provided. Two ormore layers of the sheets may be provided by repeating the steps ofundercoating, affixing the sheet, and overcoating a desired number oftimes.

[0100] An example of the reinforcing method according to the presentinvention using a fiber-reinforced plastic plate as sheet (a) isdiscussed with reference to FIG. 6.

[0101] As in the example of the working process shown in FIG. 5, thereinforcing method of the present invention may be performed, first, bypretreating the surface of structure 11 to be reinforced, marking,forming primer layer 12, and smoothing the unevenness on the layersurface, as desired. Then flexible material layer 13 is formed,optionally the surface of the flexible material layer 13 is modified,and an undercoating layer (not shown) is formed as desired.Fiber-reinforced plastic plate 15′ is affixed to the flexible materiallayer 13 with an adhesive, followed by formation of a finishing layer(protective layer) 17.

[0102] The adhesive for affixing the fiber-reinforced plastic plate 15′is preferably capable of providing a bonding strength between theflexible material layer and the plate 15′ well greater than the tensilestrength of the concrete.

[0103] The adhesive may contain a resin such as a thermosetting or roomtemperature-setting resin, with the latter being preferred for itshandleability. Examples of the thermosetting and thermoplastic resinsinclude those mentioned above, from which a suitable one may be selectedfor use. The adhesive may also contain, in addition to the resin, asuitable filler or thixotropic agent in order to maintain the adhesivewithin a suitable viscosity range or to prevent sagging uponapplication, as long as the objects of the present invention areachieved. Examples of such filler and thixotropic agent include thosementioned above, from which suitable ones may be selected for use. Thecontent of the filler and/or thixotropic agent in the adhesive ispreferably 1 to 20 wt %.

[0104] When the adhesive contains a room temperature-setting resin, thepot life of the resin is preferably 30 minutes to 5 hours, morepreferably 30 minutes to 2 hours in view of the handleability of theadhesive. The time required for curing a painted layer of the adhesiveat 20° C. is preferably 1 to 24 hours, more preferably 1 to 12 hours inview of work schedule.

[0105] The adhesive may be applied by means of a roller brush, rubberspatula, or the like tool, so that usually 0.05 to 3 kg/m², preferably0.2 to 2 kg/m² of the adhesive is applied uniformly.

[0106] In the example of the working process discussed above, only onelayer of the fiber-reinforced plastic plate is provided. However, in thepresent reinforcing method, two or more layers of the fiber-reinforcedplastic plates may also be provided. Two or more layers of the platesmay be provided by repeating the step of affixing the plastic plate withthe adhesive a desired number of times.

[0107] The structure reinforcement of the present invention is a memberfor reinforcing concrete or steel structures, and has a flexiblematerial layer and a sheet containing reinforcing fiber yarns. Theflexible material layer has a tensile elongation of 10 to 200% atmaximum load at 23° C., and a tensile strength of 0.1 to 50 N/mm² at 23°C. The flexible material and the sheet containing reinforcing fiberyarns are the same as the flexible material and sheet (a) mentionedabove. The structure reinforcement may optionally have other layers andmaterials mentioned above, as desired.

[0108] By means of the reinforcing method or the structure reinforcementof the present invention, existing structures may be reinforced easily.In reinforcing an existing road tunnel, for example, it is not necessaryto close the tunnel, and the lanes for one way may be opened duringworking. Further, the tunnel may be subjected to use immediately afterthe completion of the work.

[0109] Affixing the structure reinforcement may be followed by drivingearth anchors through the structure reinforcement into the ground atparticular intervals, and fixing the anchor heads with iron plates orbolts. The earth anchors may alternatively be driven into the groundprior to the affixing of the structure reinforcement or sheet (a). Bycombining the present invention with earth anchors, further safety isensured in preventing concrete blocks from flaking.

[0110] The above working process is usually executed using a dedicatedconstruction plant having carriages, depending on the size of thesectional area of a structure to be reinforced, as well as the range,scale, and conditions of construction. However, the working process mayalso be executed by means of robotized machinery or man power, usingcarriages of general use and temporary scaffolding. When the structureto be reinforced has a large sectional area, the working process may beexecuted mechanically, using a robot that is capable of affixing thestructure reinforcement or sheet (a) and of applying the epoxy resin.

[0111] By combining the structure reinforcement of the present inventionwith ground reinforcement with anchor members, suspension of thestructure, or arch setting, or with injection of a void filler forconcrete surface or a soil improving agent into the concrete liner orthe ground, the internal stress acting on the concrete liner isbalanced, and the reinforcing effect may further be improved.

[0112] The reinforcing method of the present invention may be adoptedquite flexibly to the degree and scale of reinforcement required by thestructure, may be executed using a temporary plant of a relatively smallscale, and may be adopted to a variety of special works under variousconditions.

[0113] The structure reinforcement of the present invention may befabricated on site during working as mentioned above, or alternatively,may be fabricated in advance as a laminate which has been cured andshaped into a desired size and thickness, and affixed to the structuresurface via an adhesive layer and the like.

[0114] The reinforced structure according to the present invention is astructure wherein the above structure reinforcement has been providedover the surface of a concrete or steel structure to be reinforced, withthe flexible material layer of the structure reinforcement interposedbetween the structure surface and the sheet containing reinforcing fiberyarns, and includes structures reinforced by the above reinforcingmethod. When the reinforced structure has a curved surface on its innerwall, it is preferred that the structure reinforcement has been providedat least over the curved surface on the inner wall of the structure,with the reinforcing fiber yarns of sheet (a) of the structurereinforcement arranged along the curvature of the curved surface, andwith the flexible material layer of the structure reinforcementinterposed between sheet (a) and the inner wall surface of thestructure. When the reinforced structure has an annular inner wallsurface, it is preferred that the structure reinforcement has beenprovided continuously in the circumferential direction of the inner wallsurface over at least a portion of the length of the structure, with thereinforcing fiber yarns of sheet (a) of the structure reinforcementarranged in the circumferential direction of the annular inner wall, andwith the flexible material layer of the structure reinforcementinterposed between sheet (a) and the inner wall surface of thestructure.

[0115] An example of the reinforced structure 70 according to thepresent invention is shown in FIG. 7, which has a curved surface on itsinner wall.

[0116] The reinforced structure 70 has structure 71 having alongitudinally-extending curved surface, and primer layer 72, flexiblematerial layer 73, undercoating layer 74, sheet 75 as sheet (a),overcoating layer 76, and surface finishing layer 77 formed in thisorder outwardly from the curved inner wall surface of the structure 71.

[0117] In the reinforced structure 70, only one layer of the sheetcontaining reinforcing fiber yarns has been provided. However, accordingto the present invention, two or more layers of the sheets containingreinforcing fiber yarns may also be provided. Two or more layers of thesheets may be provided by repeating the steps of undercoating, affixingthe reinforcing fiber sheet, and overcoating a desired number of times.

[0118] The reinforced structure having the structure reinforcement thusformed on its curved surface, exhibits strength and rigidity a couple oftimes greater than those of a structure provided with a conventionalsheet containing reinforcing fiber yarns. The reinforced structures ofthe present invention having the reinforcing fiber yarns of the sheetarranged along the curvature or along the circumference, are given stillimproved reinforcing effect. In particular, when a structure reinforcedto be the reinforced structure has an annular inner wall surface, thestructure reinforcement of the present invention has been provided overthe entire or a portion of the length of the structure, with thereinforcing fiber yarns of the sheet of the structure reinforcementarranged continuously in the circumferential direction of the annularinner wall surface. Thus the reinforced structure exhibits an excellentproperty against tensile stress, compared to a corresponding structureprovided with a conventional sheet containing reinforcing fiber yarns.

[0119] According to the reinforcing method of the present inventiondiscussed heretofore, sheet (a) is provided over the surface of astructure to be reinforced, with the particular flexible materialinterposed therebetween, so that the structure and the sheet containingreinforcing fiber yarn is stably integrated, sheet (a) is prevented frombeing separated, and sufficient reinforcement is easily and convenientlygiven by maximum use of the strength of sheet (a). Further, sheet (a)for structure reinforcing according to the present invention exhibits,when used in the present reinforcing method, its maximum strengthwithout being separated from the structure, and conveniently facilitatessufficient reinforcement. The structure reinforcement according to thepresent invention exhibits its maximum strength without being separated,and conveniently facilitates sufficient reinforcement.

EXAMPLES

[0120] The present invention will now be explained in further detailwith reference to Examples and Comparative Examples, but the presentinvention is not limited thereto.

Example 1-1

[0121] A concrete test piece having main reinforcements and hoopsarranged therein was reinforced in accordance with the reinforcingmethod of the present invention using the flexible material and thesheet containing reinforcing fiber yarns, and tested for its reinforcingeffect.

[0122] As a test piece, beam 80 shown in FIG. 8 was used, which was 2200mm long, 200 mm wide, and 200 mm high. The beam 80 had four SD295 steelbars of D13 as main reinforcements 81, and SD295 steel bars of D6 ashoops 82 arranged at 150 mm intervals. On the bottom 83 of the testpiece, an epoxy primer was applied for 1740 mm of the length (middleportion) over the entire width, to thereby form a primer layer (notshown). Then an epoxy flexible material (epoxy resin, trade name“TOHODITE EE50”, manufactured by TOHO EARTHTECH, INC.; tensileelongation at maximum load at 23° C.: 95% (measured in accordance withJIS K7113) , tensile strength at 23° C.: 1.4 N/mm² (measured inaccordance with JIS K74113) , tensile elongation at maximum load at 5°C.: 65%, tensile strength at 5° C: 6.5 N/mm², all in cured state) wasapplied to form flexible material layer 84 of 500 μm thick. Further, onelayer of sheets 85 containing reinforcing fiber yarns (trade name“HT300”, manufactured by NIPPON MITSUBISHI OIL CORPORATION) was affixedwith a room temperature-setting epoxy resin so that the reinforcingfiber yarns are directed in the longitudinal direction of the mainreinforcements.

[0123] After curing for more than one week from the affixation of thesheets 85, a static loading test was conducted by bringing supportingpoints 86 into contact with the test piece as shown in FIG. 8, with 1800mm distance between the supporting points and 300 mm distance betweenthe loading points, and applying four-point monotonous load. Thebreaking load, maximum displacement, and maximum strain of the sheets 85as measured, as well as the form of breaking of the sheets 85 observedat break are shown in Table 1. Further, the strain distribution of thesheet containing reinforcing fiber yarns (relationship between thedistance from the center of the test piece and the strain) were measuredfor various loads. The results are shown in FIG. 9. The relationshipbetween the applied load and the displacement are shown in FIG. 10.

Example 1-2

[0124] A concrete test piece having main reinforcements and hoopsarranged therein was reinforced in accordance with the reinforcingmethod of the present invention using the flexible material and thesheet containing reinforcing fiber yarns, and tested for its reinforcingeffect.

[0125] As a test piece, a beam as used in Example 1-1 was used. Thesheets 85 was replaced with fiber-reinforced plastic plate 85, which wasTU plate TYPE-S (trade name, manufactured by NIPPON MITSUBISHI OILCORPORATION).

[0126] On the bottom of the test piece, the epoxy primer as used inExample 1-1 was applied for 1740 mm of the length (middle portion) overthe entire width, to thereby form a primer layer. Then an epoxy flexiblematerial (epoxy resin, trade name “TOHODITE EE50” manufactured by TOHOEARTHTECH, INC.; tensile elongation at maximum load at 23° C.: 95%(measured in accordance with JIS K7113), tensile strength at 23° C.: 1.4N/mm² (measured in accordance with JIS K7113), tensile elongation atmaximum load at 5° C.: 65%, tensile strength that 5° C.: 6.5 N/mm², allin cured state) was applied to form a flexible material layer of 500 μmthick. Further, one sheet of the fiber-reinforced plastic plate 85 wasaffixed with the room temperature-setting epoxy resin as used in Example1-1 so that the reinforcing fibers are directed in the longitudinaldirection of the main reinforcements.

[0127] After curing for more than one week from the affixation of theplastic plate, a static loading test was conducted by applyingfour-point monotonous load to the test piece, with 1800 mm distancebetween the supporting points and 300 mm distance between the loadingpoints. The breaking load, maximum displacement, and maximum strain ofthe sheet containing reinforcing fibers as measured, as well as the formof breaking of the sheet observed at break are shown in Table 1.

Example 1-3

[0128] The static loading test was conducted in the same way as inExample 1-1, except that the flexible material layer 84 was formed in1000 μm thickness. The results are shown in Table 1 and FIG. 10.

Example 1-4

[0129] A test piece was reinforced in accordance with the reinforcingmethod of the present invention in the same way as in Example 1-1,except that the flexible material was replaced with EE50W (epoxy resin,trade name “TOHODITE EE50W”, manufactured by TOHO EARTHTECH, INC.;tensile elongation at maximum load at 23° C.: 56% (measured inaccordance with JIS K7113) , tensile strength at 23° C.: 1.2 N/mm²(measured in accordance with JIS K7113), tensile elongation at maximumload at 5° C.: 55%, tensile strength at 5° C.: 5 N/mm², all in curedstate), and the static loading test was conducted. The breaking load,maximum displacement, and maximum strain of the sheet containingreinforcing fibers, as well as the form of breaking of the sheetobserved at break are shown in Table 1. TABLE 1 Maximum strain Form ofof sheet breaking containing of sheet Breaking Maximum reinforcingcontaining load displacement fiber yarns reinforcing (kN) (mm) (μ) fiberyarns Example 1-1 98.9 34 14757 broken Example 1-2 97.8 34 14624 brokenExample 1-3 97.4 30 13848 broken Example 1-4 96.9 28 13279 broken

Comparative Example 1-1

[0130] The static loading test was conducted in the same way as inExample 1-1 on a test piece as used in Example 1-1 but without anyreinforcement. The results are shown in Table 2 and FIG. 10.

Comparative Example 1-2

[0131] A test piece was reinforced in the same way as in Example 1-1,except that the flexible material layer was not formed, and the staticloading test was conducted in the same way as in Example 1-1. Theresults are shown in Table 2 and FIGS. 10 and 11.

Comparative Example 1-3

[0132] A test piece was reinforced in the same way as in Example 1-1,except that the flexible material was replaced with a flexible materiallayer of an epoxy resin (tensile elongation at maximum load at 23° C.:5% (measured in accordance with JIS K7113), tensile strength at 23° C.:40 N/mm² (measured in accordance with JIS K7113), and the static loadingtest was conducted in the same way as in Example 1-1. The results areshown in Table 2 and FIG. 10. TABLE 2 Maximum strain Form of of sheetbreaking containing of sheet Breaking Maximum reinforcing containingload displacement fiber yarns reinforcing (kN) (mm) (μ) fiber yarnsComparative 441 24 — — Example 1-1 Comparative 78.3 22 7790 separatedExample 1-2 Comparative 76.4 23 7840 separated Example 1-3

Example 2-1

[0133] A steel test piece was reinforced in accordance with thereinforcing method of the present invention using the flexible materialand the sheet containing reinforcing fiber yarns, and tested for itsreinforcing method.

[0134] As a test piece, I steel 21 for beam shown in FIG. 12 was used,which was 200 mm×100 mm×2000 mm in size. The I steel 21 was reinforcedat loading points and supporting points with steel plates 22 of 5.5 mmthick. On the bottom 23 of the test piece, an epoxy primer was appliedfor 1600 mm of the length (middle portion) over the entire width, tothereby form a primer layer (not shown). Then an epoxy flexible material(epoxy resin, trade name “TOHODITE EE50”, manufactured by TOHOEARTHTECH, INC.; tensile elongation at maximum load at 23° C.: 95%(measured in accordance with JIS K7131), tensile strength at 23° C.: 1.4N/mm² (measured in accordance with JIS K7131), tensile elongation atmaximum load at 5° C.: 65%, tensile strength at 5° C.: 6.5 N/mm², all incured state) was applied to form flexible material layer 24 of 500 μmthick. Further, five layers of sheets 25 containing reinforcing fiberyarns (trade name “HT300”, manufactured by NIPPON MITSUBISHI OILCORPORATION) were affixed with a room temperature-setting epoxy resin sothat the reinforcing fibers are directed in the longitudinal direction.After curing for more than one week after the affixation of the sheets25, a static loading test was conducted by bringing supporting points 26into contact with the test piece I steel 21 as shown in FIG. 12, with1800 mm distance between the supporting points, and applying monotonousload. The breaking load and maximum displacement as measured are shownin Table 3.

Example 2-2

[0135] A steel test piece was reinforced in accordance with thereinforcing method of the present invention using the flexible materialand the fiber-reinforced plastic plate, and tested for its reinforcingmethod.

[0136] As a test piece, an I steel as used in Example 2-1 was used. Thesheets 25 were replaced with fiber-reinforced plastic plates 25, whichwere TU plate TYPE-S (trade name, manufactured by NIPPON MITSUBISHI OILCORPORATION). On the bottom of the test piece, the epoxy primer as usedin Example 2-1 was applied for 1600 mm of the length (middle portion)over the entire width, to thereby form a primer layer. Then an epoxyflexible material (epoxy resin, trade name “TOHODITE EE50” manufacturedby TOHO EARTHTECH, INC.; tensile elongation at maximum load at 23° C.:95% (measured in accordance with JIS K7113), tensile strength at 23° C.:1.4 N/mm² (measured in accordance with JIS K7131) both in cured state)was applied to form flexible material layer 24 of 500 μm thick. Further,five sheets of the fiber-reinforced plastic plates 25 were affixed withthe room temperature-setting epoxy resin as used in Example 2-1 so thatthe reinforcing fibers are directed in the longitudinal direction. Aftercuring for more than one week from the affixation of the plastic plates25, a static loading test was conducted by bringing supporting points 26into contact with the I steel 21, with 1800 mm distance between theloading points, and applying monotonous load. As a result, goodreinforcing effect was observed.

Comparative Example 2-1

[0137] The static loading test was conducted in the same way as inExample 2-1 on a test piece as used in Example 2-1 but without anyreinforcement. The results are shown in Table 3.

Comparative Example 2-2

[0138] The static loading test was conducted in the same way as inExample 2-1, except that the flexible material layer 24 was not formed.The results are shown in Table 3. TABLE 3 Breaking load Maximumdisplacement (kN) (mm) Example 2-1 19.1 18.4 Comparative 17.0 58.0Example 2-1 Comparative 17.5 16.9 Example 2-2

Example 3-1

[0139] A concrete Hume pipe (JIS A5303B, Type 1; inner diameter: 1200mm, thickness: 95 mm, length: 2430 mm) was cleaned on its inner wall byhigh pressure water jet, and an epoxy primer was applied all over theinner wall to form a primer layer.

[0140] Then 600 g/m² of a starting material for an epoxy flexiblematerial (EE50 manufactured by TOHO EARTHTECH, INC.) was applied allover the inner wall to form a flexible material layer of 500 μm thick. Amolded product prepared in the same way as for this flexible materiallayer was measured for its properties, to exhibit 95% tensile elongationat maximum load and 1.4 N/mm² tensile strength, both measured at 23° C.in accordance with JIS K7113, and 65% tensile elongation at maximum loadand 6.5 N/mm² tensile strength, both measured at 5° C. in accordancewith JIS K 7113.

[0141] Next, a matrix resin (trade name “BOND E 2500”, manufactured byKONISHI CO., LTD.) was applied over the flexible material layer by meansof a roller, and the surface was lined with reinforcing fiber sheets (TUCloth ST 200-50, manufactured by NIPPON MITSUBISHI CORPORATION, fiberarea weight: 200 g/m²; sheet width: 50 mm; design thickness: 0.11 mm;tensile strength: 3430 N/mm²; tensile modulus of elasticity: 2.3×10⁵N/mm²). The sheets containing reinforcing fiber yarns were arranged inthe circumferential direction of the Hume pipe, and pressed with animpregnation roller. As a result, the sheets were embedded in the matrixresin. The application of the matrix resin and the laminating with thesheets were repeated, to form two layers of the sheets containingreinforcing fiber yarns all over the inner wall of the Hume pipe.

[0142] The reinforced Hume pipe thus obtained was subjected to a loadingtest in accordance with JIS A5303 “Centrifugal Reinforced ConcretePipe”, wherein load P was applied until the pipe breaks. The structureof the reinforcement and the outline of the test are shown in FIGS. 13and 14, and the results are shown in Table 4. Incidentally, in FIGS. 13and 14, the reference numeral 32 refers to the concrete Hume pipe, 33 tothe flexible material layer, 34 to the reinforcing fiber sheets, and 31to a jig for loading.

[0143] The resulting reinforced Hume pipe was observed to have animproved durability compared to a non-reinforced Hume pipe, and thetensile stress generated on the top and bottom of the pipe was observedto be dispersed in the circumferential directions of the pipe by meansof the flexible material layer. It was demonstrated that the reinforcedHume pipe had properties superior to those of Comparative Examples to bediscussed below.

Comparative Example 3-1

[0144] A reinforced Hume pipe was prepared in the same way as in Example3-1, except that the flexible material layer was not formed, and theloading test was conducted. The results are shown in Table 4.

Comparative Example 3-2

[0145] The loading test was conducted in the same way as in Example 1 onthe Hume pipe before reinforcement as used in Example 3-1. The resultsare shown in Table 4. TABLE 4 Comparative Comparative Example 3-1Example 3-1 Example 3-2 Number of laminated layers 2 2 0 of sheetscontaining reinforcing fiber yarns Flexible material present absentabsent layer Maximum load 466 398 354 (kN) Ratio of the reinforced 1.321.12 — to the non-reinforced

Example 3-2

[0146] A concrete Hume pipe (JIS A 5303 B, Type 1; inner diameter: 1200mm, thickness: 95 mm, length: 2430 mm) was cut to obtain an exactlysemicylindrical Hume pipe.

[0147] This semicylindrical Hume pipe was cleaned on its inner wall byhigh pressure water jet, and an epoxy primer was applied all over theinner wall to form a primer layer.

[0148] Then 600 g/m² of a starting material for an epoxy flexiblematerial (EE50 manufactured by TOHO EARTHTECH, INC.) was applied allover the inner wall to form a flexible material layer of 500 μm thick. Amolded product prepared in the same way as for this flexible materiallayer was measured for its properties, to exhibit 95% tensile elongationat maximum load and 1.4 N/mm² tensile strength, both measured inaccordance with JIS K7113, and 1.5 N/mm² tensile modulus of elasticitymeasured in accordance with JIS K7113, all at 23° C., and 65% tensileelongation at maximum load and 6.5 N/mm² tensile strength, both measuredat 5° C. in accordance with JIS K 7113.

[0149] Next, a matrix resin (trade name “BOND E 2500”, manufactured byKONISHI CO., LTD.) was applied over the flexible material layer by meansof a roller, and the surface was lined with reinforcing fiber sheets (TUCloth WT 200-50, manufactured by NIPPON MITSUBISHI OIL CORPORATION,fiber area weight: 200 g/m², sheet width: 50 mm, design thickness: 0.11mm, tensile strength: 3430 N/mm², tensile modulus of elasticity: 2.3×10⁵N/mm²). The sheets containing reinforcing fiber yarns were arranged inthe circumferential direction of the Hume pipe, and pressed with animpregnation roller. As a result, the sheets were embedded in the matrixresin. The application of the matrix resin and the laminating with thesheets containing reinforcing fiber yarns were repeated, to form twolayers of the sheets containing reinforcing fiber yarns all over theinner wall of the Hume pipe.

[0150] The reinforced semicylindrical Hume pipe thus obtained wassubjected to a loading test in accordance with JIS A5303 “CentrifugalReinforced Concrete Pipe”, wherein load P was applied until the pipebreaks. The structure of the reinforcement and the outline of the testare shown in FIGS. 15 and 16, and the results are shown in Table 5.Incidentally, in FIGS. 15 and 16, the reference numeral 52 refers to thesemicylindrical concrete Hume Pipe, 53 to the flexible material layer,54 to the reinforcing fiber sheets, and 51 to a jig for loading.

[0151] The resulting reinforced Hume pipe was observed to have animproved durability compared to a non-reinforced Hume pipe, and thetensile stress generated on the top and bottom of the pipe was observedto be dispersed in the circumferential directions of the pipe by meansof to the flexible material layer. It was demonstrated that thereinforced Hume pipe had properties superior to those of ComparativeExamples to be discussed below.

Comparative Example 3-3

[0152] A reinforced semicylindrical Hume pipe was prepared in the sameway as in Example 3-2, except that the flexible material layer was notformed, and the loading test was conducted. The results are shown inTable 5.

Comparative Example 3-4

[0153] The loading test was conducted in the same way as in Example 3-2on the semicylindrical Hume pipe before reinforcement as used in Example3-2. The results are shown in Table 4. TABLE 5 Comparative ComparativeExample 3-2 Example 3-3 Example 3-4 Number of laminated layers 2 2 0 ofsheets containing reinforcing fiber yarns Flexible material presentabsent absent layer Maximum load 409 339 302 (kN) Ratio of thereinforced 1.35 1.12 — to the non-reinforced

What is claimed is:
 1. A method for reinforcing a structure comprisingthe step (A) of providing a sheet containing reinforcing fiber yarnsover a surface of a structure selected from the group consisting ofconcrete and steel structures, with a flexible material interposedtherebetween, said flexible material having a tensile elongation of 10to 200% at maximum load at 23° C., and a tensile strength of 0.1 to 50N/mm² at 23° C.
 2. The method of claim 1, wherein said structure isselected from the group consisting of beams, columns, slabs, slabs,stacks, RC beams, tunnels, pipes, tubes, ducts, conduits, bridges havinga curved surface, and U-shaped gutters.
 3. The method of claim 1,wherein said structure has a curved surface on its inner wall, andwherein said step (A) comprises providing said sheet containingreinforcing fiber yarns at least over said curved surface on the innerwall of said structure, with said flexible material interposedtherebetween, so that said reinforcing fiber yarns of said sheet arearranged along a curvature of said curved surface.
 4. The method ofclaim 1, wherein said structure has an annular inner wall surface, andwherein said step (A) comprises providing said sheet containingreinforcing fiber yarns continuously in a circumferential direction ofsaid inner wall surface over at least a portion of a length of saidstructure, with said flexible material interposed therebetween, so thatsaid reinforcing fiber yarns of said sheet are arranged in acircumferential direction of said annular inner wall.
 5. The method ofclaim 1, wherein said flexible material has a tensile elongation of 10to 200% at maximum load at 5 ° C., and a tensile strength of 0.1 to 50N/mm² at 5° C.
 6. The method of claim 1, wherein said flexible materialcomprises 50 to 100 wt % of a resin and 0 to 50 wt % of a filler, saidresin having a tensile modulus of elasticity of 0.1 to 50 N/mm² at 23°C. when cured.
 7. The method of claim 1, wherein said flexible materialcomprises 50 to 100 wt % of a resin and 0 to 50 wt % of a filler, saidresin having a tensile modulus of elasticity of 0.1 to 50 N/mm² at 5° C.when cured.
 8. A structure-reinforcing sheet containing reinforcingfiber yarns, wherein said structure-reinforcing sheet is a sheetcontaining reinforcing fiber yarns for use in a reinforcing method ofclaim 1, and comprises a reinforcing material having a plurality oflongitudinal reinforcing fiber yarns arranged parallel to each other ina longitudinal direction of said sheet.
 9. The sheet containingreinforcing fiber yarns of claim 8, wherein said reinforcing materialfurther has a plurality of transverse threads arranged parallel to eachother in a transverse direction of said sheet, said transverse threadsbeing selected from the group consisting of transverse reinforcing fiberyarns and transverse supplementary threads, and wherein saidlongitudinal reinforcing fiber yarns and said transverse threads form awoven structure.
 10. The sheet containing reinforcing fiber yarns ofclaim 9, wherein said longitudinal reinforcing fiber yarns and saidtransverse threads are stuck and fixed to each other with fixingmembers.
 11. The sheet containing reinforcing fiber yarns of claim 8,wherein said reinforcing material further has a plurality oflongitudinal supplementary threads arranged parallel to each other in alongitudinal direction of said sheet, and a plurality of transversesupplementary threads arranged parallel to each other in a transversedirection of said sheet, said reinforcing material having a wovenstructure wherein said longitudinal reinforcing fiber yarns aresubstantially not bent with said longitudinal and transversesupplementary threads.
 12. The sheet containing reinforcing fiber yarnsof claim 8 comprising said reinforcing material and a support forsupporting said reinforcing material, wherein said reinforcing materialis affixed to said support by means of a binder.
 13. A structurereinforcement for reinforcing a structure selected from the groupconsisting of concrete and steel structures, said reinforcementcomprising a flexible material layer and a sheet containing reinforcingfiber yarns, said flexible material layer having a tensile elongation of10 to 200% at maximum load at 23° C., and a tensile strength of 0.1 to50 N/mm² at 23° C.
 14. A reinforced structure wherein a structurereinforcement of claim 13 is provided over a surface of a structureselected from the group consisting of concrete and steel structures,with a flexible material layer of said structure reinforcementinterposed between the surface of the structure and a sheet containingreinforcing fiber yarns of said structure reinforcement.
 15. Thereinforced structure of claim 14, wherein said structure has a curvedsurface on its inner wall, and wherein said structure reinforcement isprovided at least over said curved surface on the inner wall of saidstructure, with said reinforcing fiber yarns of the sheet of thestructure reinforcement arranged along a curvature of said curvedsurface, and with said flexible material layer of the structurereinforcement interposed between said sheet and the surface of the innerwall of the structure.
 16. The reinforced structure of claim 14, whereinsaid structure has an annular inner wall surface, and wherein saidstructure reinforcement is provided continuously in a circumferentialdirection of said inner wall surface over at least a portion of a lengthof said structure, with said reinforcing fiber yarns of the sheet of thestructure reinforcement arranged in a circumferential direction of theannular inner wall, and with said flexible material layer of thestructure reinforcement interposed between said sheet and the inner wallsurface of the structure.